Lung cancer is a main cause of cancer deaths in economically well-developed countries. Above all, adenocarcinoma is a histological subtype that occurs most frequently.
The present inventors have previously reported that sustained expression of TTF-1, a lineage-specific transcription factor important for lung branching morphogenesis and physiological functions, is closely linked to lung adenocarcinoma (NPL 1). In addition, other three groups have also reached the same conclusion that TTF-1 is a lineage-survival oncogene through, for example, genome-scale searching of focal genome abnormalities in lung adenocarcinoma (NPLs 2 to 4). Since TTF-1 is essential for surfactant-protein production and physiological functions in normal adult lungs, identifying downstream molecules involved in lineage-specific survival signaling by TTF-1 is important for development of novel treatment methods.
As a result of the effort to identify such downstream molecules, the present inventors have succeeded in identifying an ROR1 (receptor tyrosine kinase-like orphan receptor 1) gene as a gene whose expression is induced by TTF-1. Then, the inventors have revealed that it is possible to inhibit the growth of specific cancer cells by suppressing the ROR1 gene expression (PTL 1).
Nevertheless, until now, there have been very little findings about the mechanism of how ROR1 suppresses cancer cell growth.